UC Riverside

Continuous downscaling in microelectronics has pushed conventional CMOS technology to its physical limits, while Moore's Law has correctly predicted the trend for decades, each step forward is accompanied with unprecedented technological difficulties and near-exponential increase in cost. At the same time, however, demands for low-power, low-cost and high-speed devices have never diminished, instead, even more stringent requirements have been imposed on device performances. It is therefore crucial to explore alternative materials and device architectures in order to alleviate the pressure caused by downscaling. To this end, we investigated two different approaches: (1) InSb nanowire based field effect transistors (NWFETs) and (2) single walled carbon nanotube (SWCNT) - peptide nucleic acid (PNA) -SWCNT conjugate.

Two types of InSb nanowires were synthesized by template-assisted electrochemistry and chemical vapor deposition (CVD) respectively. In both cases, NWFETs were fabricated by electron beam lithography (EBL) and crystallinity was confirmed by transmission electron microscopy (TEM) and selected area diffraction (SAD) patterns. For electrochemistry nanowire, ambipolar conduction was observed with strong p-type conduction, the effect of thermal annealing on the conductivity was analyzed, a NWFET model that took into consideration the underlapped region in top-gated NWFET was proposed. Hole mobility in the channel was calculated to be 292.84 cm2V-1s-1 with a density of 1.5×1017/cm3. For CVD nanowire, the diameter was below 40nm with an average of 20nm. Vapor-liquid-solid (VLS) process was speculated to be the mechanism responsible for nanowire growth. The efficient gate control was manifested by high ION/IOFF ratio which was on the order of 106 and a small inverse subthreshold slope (<200 mV/decade). Scale analysis was used to successfully account for disparities observed among a number of sample devices. N-type conduction was found in all NWFETs with electron mobility between 110 cm2*V-1*s-1 and 169 cm2*V-1*s-1.

In the approach of SWCNT-PNA-SWCNT conjugate, we chemically functionalized single walled carbon nanotubes to synthesize the conjugate and characterized its electrical properties. Negative differential resistance (NDR) was observed consistently at different temperatures and the mechanism was explained through the energy band diagram in which NDR effect was caused by misalignment between Fermi energy level at the source and resonance states in the potential well. The consistent NDR effect shows possible application for microelectronic devices.